There have been a number of suggestions in the art of transducer design in order to make loudspeaker systems more accurate in reproducing audio signals or at least more pleasing to a listener. Such designs include, generally, direct radiators and horns. Direct radiators include electro dynamic, electro static, piezo electric and ionic transducers. Most common among this group are transducers having electro dynamic motor assemblies consisting of a voice coil immersed in a magnetic field used to drive a plastic, paper or metallic diaphragm. When alternating current at audio frequencies is passed through the voice coil of such a transducer, the resulting motion is transferred to the diaphragm which then acts upon the air to produce sound waves. The present invention represents a marked departure from previously available transducer designs but is, generally, a transducer having the above-described electro dynamic motor.
Electro dynamic transducers have been described in the past as those in which the diaphragm is intended to move pistonically or isophasically and those in which the diaphragm is intended to bend, thus not acting as a rigid piston. Electro dynamic transducers in which the diaphragms move pistonically are by far the most commonly employed transducers in the audio industry although actual piston operation is seldom achieved over the entire operating range of the transducer.
Although bending wave transducers have been suggested by a wide variety of manufacturers, their use in the audio industry is rare. Bending wave transducers can generally be divided into categories such as those employing flat diaphragms and those in which the diaphragms are curved. Flat diaphragm devices are exemplified by the products of Mellrichstadt Manger. This transducer was developed by Joseph Manger in the mid 1970's and is currently in commercial production. NXT, a company based in England, has recently done extensive work in what they term a “distributed mode loudspeaker” which employs a flat bending-wave design often using multiple motors with the express objective of producing inherently diffuse radiation.
Curved diaphragm devices, although not as common as transducers employing diaphragms operating pistonically, have been used somewhat successfully in the audio industry. Such curved diaphragm transducers have taken on many forms with respect to both the shape and curvature of the diaphragm as well as the particular configuration of its motor assembly. The most recent evolution of such a product can be found in U.S. Pat. No. 6,061,461 and variations of this curved diaphragm design can be seen in the art cited in the '461 disclosure.
Virtually all curved diaphragm bending wave transducers employ diaphragms curved in only two dimensions. In the 1960's, a third type of bending wave loudspeaker was suggested by Walsh and commercialized as the Ohm loudspeaker. In fact, the Walsh design is currently manufactured by German Physiks. The Walsh transducer employs a diaphragm in the shape of an upright truncated circular cone driven by a voice coil at its small end and terminated at its large end. It has been observed that the cone does not operate as a piston but rather in a bending mode where flexural waves travel down the structure of the cone and the resulting lateral motions of the material caused a radially propagated sound wave.
A further example of a bending-wave transducer was introduced by a German company by the name of MBL. The MBL transducer employs strips or segments oriented vertically and bent. These segments are oriented with respect to one another but not joined. One “pole” of the segments is stationary and the other “pole” is driven by a conventional voice-coil motor. The attempt is to approximate a pulsating sphere. Radiation emanates from this transducer by isophasic motions of the segments.
Although most commonly employed transducers employ diaphragms which operate pistonically, there are certain inherent advantages achievable from bending wave transducers. Initially, it is noted that such transducers are not very reactive. As such, once energy is imparted to the diaphragm, it is dissipated in the bending motion rather than being stored. Further, depending upon the exact manner in which force is imparted to the diaphragm, motions of the diaphragm may be made to be mildly chaotic in which case there is some inherent diffuseness to the radiation. This has the desirable effect of allowing a large radiating area without the narrowing of the radiation angle which would normally occur. The large radiating area in turn results in a low surface loudness which is generally associated with the perceptible reports of transparency and clarity of sound emanating from such a transducer.
It has been observed that, particularly at high frequencies, even transducers which are intended to operate pistonically seldom actually achieve isophasic operation. Seeking isophasic behavior has led to extreme design approaches. On the other hand, bending-wave transducers exploit the non-rigidity of the diaphragm material thus working with the material rather than fighting against it.
It is thus an object of the present invention to provide a transducer intended to operate isophasically and yet do so at all frequency ranges, particularly at high frequency.
It is a further object of the present invention to provide a transducer capable of generating acoustic energy omni directionally in a horizontal plane.
These and further objects will be more readily apparent when considering the following disclosure and appended claims.